Effects of spark energy and energy losses to electrodes and radiation on flame kernel development

摘要

The effects of energy transfer on measurements of flame kernel development using images of expanding spherical flames have been experimentally and theoretically studied. This study includes the effects of energy input from spark plugs into a premixed combustible mixture of fuel and air, energy transfer through conduction to spark electrodes, and radiation from flame kernel to combustion vessel wall. The amount of electrical energy across the electrodes was measured accurately and varied from 52 mJ to 1.95 J. The amount of spark energy input to the premixed methane air with different equivalence ratios was found to have significant effect on the delay time for ignition of mixture up to 1-2 ms after spark jump. Our measurements also showed that the energy losses through conduction for different size electrodes of 0.381 mm to 2.54 mm was large compared with the released combustion energy up to 5-6 ms after ignition. This can explain the slow rate of flame expansion at the beginning of ignition for thick electrodes. Finally, neither of these energy transfers had a significant contribution on the rate of flame radius expansion and consequently on its burning speed 5-6 ms after ignition.